The recycling of post-consumer plastics is expected to expand as much as ten-fold beyond the current 200 million pound per year business in less than a decade. Industrial waste recycling is and will be an even bigger business.
Accordingly, there have been many different approaches to the problem of what to do with the scrap. Some merely melt down mixtures of the plastics and mold it into useful shapes. Others classify and separate them before melting or dissolving them. Still others change the nature of the mixed plastics by chemical reaction.
An older and larger business is the recycling of newspaper and other waste paper. One problem in this business is that plastic scraps are often mixed in with the paper. Re-pulping of the paper is hampered by such scraps and their removal and disposal costs threaten the profitability of the business.
A reduction in the size of the scrap pieces facilitates melting, dissolution, and reaction. In the re-pulping of paper, some end uses of the product would permit or even benefit from the presence of comminuted plastic. One process for grinding polyethylene terephthalate (PET) bottles is limited to specific bottle designs. Another process, invented before the need for recycling became apparent and directed to the comminution of virgin plastics for use in certain applications, is taught in U.S. Pat. No. 3,150,834. There, a suspension of the plastic in water or some other non-solvating liquid that is inert to the plastic is fed between a pair of grinding surfaces, at least one of which is rotating.
In U.S. Pat. No. 2,412,586, the wet grinding of scrap rubber is taught but the use of an excessive amount of water is taught against because the formation of a slurry would reduce the grinding efficiency.
The intensive milling of a poly (arylene sulfide) in water containing a non-ionic surface active agent such as Rohm & Haas' Triton X-100 wetting agent to form a dispersion is taught in U.S. Pat. No. 3,799,454. The particle size of the plastic before being milled in a ball mill is about 30 mesh (about 24 mils) or smaller. The milling time in a ball mill is from 5 to 40 hours; use of a vibratory ball mill may reduce the time tenfold.
It is an object of this invention, therefore, to provide a quick, low-cost method for comminuting thin films or sheets of plastic.
It is a related object to provide a method for comminuting macro-sized scraps of such thin film.
It is a further related object to provide a method for comminuting a mixture of different plastics.
It is another object to provide a comminuted plastic for use as a filler.
It is another object of this invention to provide a pulp of cellulose and plastic.